ON::LengthUnitSystem::None indicates no length unit system. The scale factor
when converting between a specified unit system and None is always 1.0.
ON::LengthUnitSystem::None is used as a unit system for models and
instance defitions that should be imported or referenced with no
scaling applied.

Angstroms

12

1 angstroms = 1.0e-10 meters

Nanometers

13

1 nanometer = 1.0e-9 meters

Microns

1

1 micron = 1.0e-6 meters

Millimeters

2

1 millimeter = 1.0e-3 meters

Centimeters

3

1 centimeter = 1.0e-2 meters

Decimeters

14

1 decimeter = 1.0e-1 meters

Meters

4

SI meter length unit

Dekameters

15

1 dekameter = 1.0e+1 meters

Hectometers

16

1 hectometer = 1.0e+2 meters

Kilometers

5

1 kilometer = 1.0e+3 meters

Megameters

17

1 megameter = 1.0e+6 meters

Gigameters

18

1 gigameter = 1.0e+9 meters

Microinches

6

1 microinches = 2.54e-8 meters = 1.0e-6 inches

Mils

7

1 mil = 2.54e-5 meters = 0.001 inches

Inches

8

1 inch = 0.0254 meters = 1/12 foot

Feet

9

1 foot = 0.3048 meters (12 inches)

Yards

19

1 foot = 0.3048 meters = 12 inches

Miles

10

1 US statute mile = 1609.344 meters = 5280 feet

PrinterPoint

20

Printer distance 1/72 inches (computer points).

PrinterPica

21

Printer distance 1/6 inches (computer picas).

NauticalMile

22

Terrestrial distance, 1852 meters.

Approximately 1 minute of arc on a terrestrial great circle.
See http://en.wikipedia.org/wiki/Nautical_mile .

Astronomical

23

Astronomical unit distance.
http://en.wikipedia.org/wiki/Astronomical_unit
1.495979e+11 // http://units.nist.gov/Pubs/SP811/appenB9.htm
An astronomical unit (au) is the mean distance from the
center of the earth to the center of the sun.

A light year is the distance light travels in one Julian year.
The speed of light is exactly 299792458 meters/second.
A Julian year is exactly 365.25 * 86400 seconds and is
approximately the time it takes for one earth orbit.

1 astronomical unit = 1.4959787e+11 meters
An astronomical unit (au) is the mean distance from the
center of the earth to the center of the sun.
References:
http://en.wikipedia.org/wiki/Astronomical_unit (1.4959787e+11 meters)
http://units.nist.gov/Pubs/SP811/appenB9.htm (1.495979e+11 meters)

LightYears

24

1 light year = 9.4607304725808e+15 meters
A light year is the distance light travels in one Julian year.
The speed of light is exactly 299792458 meters/second.
A Julian year is exactly 365.25 * 86400 seconds and is
approximately the time it takes for one earth orbit.
References:
http://en.wikipedia.org/wiki/Light_year (9.4607304725808e+15 meters)
http://units.nist.gov/Pubs/SP811/appenB9.htm (9.46073e+15 meters)

CustomUnits

11

The name of a custom unit and the conversion to meters
are saved in the ON_UnitSystem class.

Unset

255

The ON::LengthUnitSystem::Unset is used to indicate no unit system is set.
This is a differnt condition from ON::LengthUnitSystem::None.